The present invention relates to an optical character reading system for reading characters, symbols and the like which are larger than the size of a sensor used in the character reading system.
A conventional optical character reading device is shown in FIG. 1. In the conventional device, the image of a character, symbol or the like (hereinafter referred to merely as "a character") 6 on a sheet 5 is formed on an image sensor 2, which is composed of photoelectric conversion elements, through an optical system 1. An analog signal produced by the sensor is converted into a binary signal having states corresponding to the white background of the sheet and the black character by a binary coding circuit 3. The binary signal is coupled to the input of a recognition circuit 4 which recognizes the various characters and produces digital output signals in accordance therewith. In this case, the image sensor 2 is electrically scanned in a vertical direction. If the image sensor 2 is a two-dimensional sensor, the sensor may be electrically scanned in the horizontal direction 8 while the optical system or the sheet is mechanically moved so as to read the characters. If the image sensor 2 is a one-dimensional sensor, then the optical system or the sheet should be mechanically moved to read the characters. The sheet 5 is irradiated by a light source, not shown.
As is clear from the above description, in order to cover a character two-dimensionally with a one-dimensional sensor, it is necessary that the image sensor 2 be moved in the horizontal direction 8 at constant speed relative to the sheet 5. In the case where the speed of the image sensor 2 relative to the sheet 5 is unknown, it is required that the white/black character pattern be stored for the entire character region. Accordingly, the storage capacity of the device must be relatively large resulting in a high manufacturing cost of the device.
Even for a two-dimensional sensor, if the speed of the image sensor relative to the sheet 5 is unknown or changed, the sensor 2 is not applicable to the case where the size of the character to be read out is larger than that of the sensor 2, for example, as shown in FIG. 2B. In this case, it is necessary either that the sensor 2 be moved at a constant speed with respect to the sheet similar to the case of a one-dimensional sensor or that the white/black patterns are stored over the entire character region. In the latter case, a memory having a large storage capacity is required.
The use of a two-dimensional sensor for reading characters of large width and requiring a large number of binary bits is disadvantageous in that a two-dimensional sensor sufficiently large in size is expensive and that the time required for the recognition process is correspondingly great.
Because of these disadvantages, heretofore it has proved difficult and uneconomical to read a character larger than the range of the sensor.
The present invention has been conceived with the intent of eliminating the above-described difficulties. An object of the invention is thus to make it simple to read and recognize a character which is larger than the range of the sensor.